RESUMO
This study reports results of analysis of sediment cores collected from the Patos Lagoon estuary. This estuary receives materials from land runoff into Patos and Mirim lagoons and from exchange with the adjacent South Atlantic Ocean through a narrow inlet. Sediment from these sources is mostly natural, but additional contributions associated with source/activities related to the port of Rio Grande. The aim of this study was to estimate rates of accumulation of the sediments and to assess the significance of metal inputs from these activities relative to natural inputs. Our results indicate an average sedimentation rate of 0.3 cm/yr and that the transport of suspended solids from offshore sources into the estuary was enhanced after the deepening of the channel and construction of the breakwaters (in the early 1900). Results for metal accumulation in these sediments suggest that there have been only minor enrichments which can be attributed to anthropogenic sources.
Assuntos
Monitoramento Ambiental , Sedimentos Geológicos/química , Poluentes Químicos da Água/análise , Poluição Química da Água/estatística & dados numéricos , Oceano Atlântico , Brasil , Humanos , Água do Mar/químicaRESUMO
In August of 1998 the tanker BAHAMAS belonging to the Chem Oil Company containing 12,000 t of concentrated sulphuric acid, had an accident on board, after which estuarine water entered one of the compartments of the tanker, resulting in a vigorous exothermic reaction. The reaction of acid with the metallic interior hull of the ship and the accompanying heat and H2 production resulted in an imminent risk of explosion. To avoid an explosion, given the fact that neutralization was not possible, some of the cargo was discharged into the surrounding water. Neutralization was done in January 1999, after the acid concentration in the tanker had decreased and the concentrations of Fe, Cr and Ni remained elevated. Metal concentrations in bottom sediments showed significant modifications. Leached mercury migrated and redeposited downstream, reaching approximately 76 times the background values. Such an anomaly has a well expressed barrier character. The mechanism for redeposition of Hg and other metals probably followed the pattern: Downstream as a result of dilution and mixing with seawater the pH of acid-water increases, favouring adsorption and/or precipitation of metals. The leading edge of a geochemical barrier, at positions 7-9 of sampling sites (Fig. 1), is confirmed by pH variations in the water. The reestablishment of normal pH occurred after a short time due to the high buffering capacity of seawater and large natural dilution process. The concentration of metals in estuarine water during and after the accident showed insignificant anomalies.
Assuntos
Sedimentos Geológicos/química , Metais Pesados/química , Ácidos Sulfúricos/química , Poluentes da Água/análise , Adsorção , Precipitação Química , Monitoramento Ambiental , Concentração de Íons de Hidrogênio , Compostos Orgânicos/análise , Movimentos da ÁguaRESUMO
The hydrogen chromate anion (HCrO4-), which is the predominant species in acidic solutions and solutions with low chromium concentration, was determined by capillary zone electrophoresis (CZE) using UV detection on-column at 200 nm. A fused-silica capillary (55 cm x 50 microm i.d.) was employed with a high negative voltage of 20 kV. Total chromium was determined after reduction by H2O2 and its complexation by EDTA. The use of H2O2 as reducing agent is advantageous, as it does not increase the conductivity of the solution. Detection limits achieved (for 200 s injection time) were 30 and 8 microg/L for Cr(VI) and Cr(III), respectively. The CZE results obtained for Cr(III) and Cr(VI) were compared with those obtained by ion exchange with subsequent AAS.